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排序方式: 共有659条查询结果,搜索用时 187 毫秒
651.
652.
Posthumus W Laven J de With G van der Linde R 《Journal of colloid and interface science》2006,304(2):394-401
The effect of the addition of antimony doped tin oxide (ATO) nanoparticles on the electrical conductivity of acrylate films is described. To enable dispersing of ATO in acrylate matrices, 3-methacryloxypropyltrimethoxysilane (MPS) was grafted on the surface of the filler. The amount of MPS used for this surface modification was found to strongly affect the electrical conductivity. Surface modification with a large amount of MPS resulted in colloidally stable dispersions of ATO, leading to a homogeneous distribution. Surface modification with small amounts of MPS led to instable ATO dispersions and aggregation of ATO into a fractal type network, which gives a much higher conductivity especially at low-volume fractions. For composites with a fractal type ATO network a second effect was found. Decreasing the amount of on ATO grafted MPS resulted in an increase of the electrical conduction between the ATO particles. 相似文献
653.
Lorenz Willmann Klaus Jungmann Cornelis J. G. Onderwater Rob G. E. Timmermans Hans W. Wilschut 《Hyperfine Interactions》2012,211(1-3):39-43
Discrete symmetries tested in high precision atomic physics experiments provide guidance to model building beyond the Standard Model (SM). Here experimental opportunities arise for searches for permanent electric dipole moments (EDMs) and measurements of atomic parity violation (APV). Heavy atoms are favorable for such experiments since symmetry violating effects in atoms increase faster than the third power of the nuclear charge Z. Of special interest are isotopes of the heavy alkaline earth element radium (Z=88) since they offer large enhancement factors for EDMs and provide a new experimental road towards high precision measurements of atomic parity violation. These opportunities are exploited at the TRIμP facility at KVI, Groningen. 相似文献
654.
Mark A. Hempenius Neil S. Robins Rob G. H. Lammertink G. Julius Vancso 《Macromolecular rapid communications》2001,22(1):30-33
The water soluble poly(ferrocenylsilane) polycation, poly(ferrocenyl(3‐ammoniumpropyl)methylsilane), was synthesized by transition metal‐catalyzed ring‐opening polymerization of the novel [1]ferrocenophane Fe(η‐C5H4)2SiCH3(CH2)3Cl and by subsequent side group modification. Amination of the chloropropyl moieties using potassium 1,1,3,3‐tetramethyldisilazide followed by acidic hydrolysis produced the polycation. The polycation was employed together with poly(sodium vinylsulfonate) in the electrostatic layer‐by‐layer self‐assembly process to form organometallic multilayers on quartz. The multilayer fabrication process was monitored using UV/Vis absorption spectroscopy and XPS. 相似文献
655.
656.
Jef R. Vanhoof Pieter J. De Smedt Jan Derhaeg Rob Ameloot Dirk E. De Vos 《Angewandte Chemie (International ed. in English)》2023,62(49):e202311539
1,2-Dioxygenation of alkenes leads to a structural motif ubiquitous in organic synthons, natural products and active pharmaceutical ingredients. Straightforward and green synthesis protocols starting from abundant raw materials are required for facile and sustainable access to these crucial moieties. Especially industrially abundant aliphatic alkenes have proven to be arduous substrates in sustainable 1,2-dioxygenation methods. Here, we report a highly efficient electrocatalytic diacetoxylation of alkenes under ambient conditions using a simple iodobenzene mediator and acetic acid as both the solvent and an atom-efficient reactant. This transition metal-free method is applicable to a wide range of alkenes, even challenging feedstock alkenes such as ethylene and propylene, with a broad functional group tolerance and excellent faradaic efficiencies up to 87 %. In addition, this protocol can be extrapolated to alkenoic acids, resulting in cyclization of the starting materials to valuable lactone derivatives. With aromatic alkenes, a competing mechanism of direct anodic oxidation exists which enables reaction under catalyst-free conditions. The synthetic method is extensively investigated with cyclic voltammetry. 相似文献
657.
Mria Pter Mark A. Hempenius Rob G.H. Lammertink Julius G. Vancso 《Macromolecular Symposia》2001,167(1):285-296
Ethylenesulfide and trimethylenesulfide end‐functionalized poly(ferrocenyldimethylsilanes) (ES‐PFS and TMS‐PFS) with different degrees of polymerization were prepared via anionic ring‐opening polymerization. Molecular characterization of ES‐PFS was carried out by using 1H‐NMR, GPC, FTIR, and elemental analysis. Thin films of ES‐PFS were prepared by immersing gold(111) substrates into 1.0 mg/ml solutions of the polymers in toluene. The polymeric films were characterized by FTIR, XPS, and contact angle measurements. Thicknesses of the grafted films were measured by SPR. Thicknesses determined by SPR and the theoretically calculated values are in a reasonable agreement. The morphology of the films was studied by tapping mode AFM. The electrochemical behavior of the films was monitored by cyclic voltammetry (CV). CVs show two reversible redox peaks, indicating a stepwise oxidation of the iron atoms in the polymer chains. Scanning Electrochemical Force Microscopy (SEFM) allowed us to study in situ the morphological changes occurring in the film upon electrochemical oxidation or reduction. AFM images indicated that in the oxidized form the chains were stretched due to electrostatic repulsion. 相似文献
658.
Andrew J. Devine Dr. Alice E. Parnell Dr. Catherine R. Back Dr. Nicholas R. Lees Dr. Samuel T. Johns Ainul Z. Zulkepli Rob Barringer Dr. Katja Zorn Dr. James E. M. Stach Prof. Matthew P. Crump Prof. Martin A. Hayes Dr. Marc W. van der Kamp Prof. Paul R. Race Prof. Christine L. Willis 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(3):e202213053
Abyssomicin C and its atropisomer are potent inhibitors of bacterial folate metabolism. They possess complex polycyclic structures, and their biosynthesis has been shown to involve several unusual enzymatic transformations. Using a combination of synthesis and in vitro assays we reveal that AbyV, a cytochrome P450 enzyme from the aby gene cluster, catalyses a key late-stage epoxidation required for the installation of the characteristic ether-bridged core of abyssomicin C. The X-ray crystal structure of AbyV has been determined, which in combination with molecular dynamics simulations provides a structural framework for our functional data. This work demonstrates the power of combining selective carbon-13 labelling with NMR spectroscopy as a sensitive tool to interrogate enzyme-catalysed reactions in vitro with no need for purification. 相似文献
659.